The unfortunate reality of aero positions is that the stronger you are, the easier it gets to hold an aero position. If you go for too aero of a position while not having the requisite power, you will get numb hands and tired arms.

BUT assuming that you get the requisite power to comfortably hold an aero position - try the following:

1) Move saddle up and forward VERY gradually. This is basically getting you closer to the TT position. More weight on the hands and pedals, less on the saddle. But it will allow for a flatter back. Revert your change if you experience hand discomfort, neck discomfort, or your hour power goes down too much (due to over fatiguing of quads)

2) get a saddle that allows for maximum rotation of the hips. Hopefully you already have this, and aren’t compensating for a lack of hip rotation with spinal flexion. At some point, most people who aren’t genetic freaks will need to resort to spinal flexion to get more aero but you should max out your hip rotation first. Stop rotating your hips once you start feeling impingement of the hip joint.

3) Get a shorter crank. Many studies have proven that the power loss from somewhat shorter cranks is negligible to nonexistent, but the comfort and aerodynamic gains are real. Find someone who you know can very easily hold an extremely aero position with a straight back. Chances are that, relative to their height, they will have short tibias or low kneecaps. Compensate for your longer tibias by going for a shorter crank. If you are 5’10” or under, you can almost certainly get away with 165mm cranks. Under 6’2”, 170. Something around that. Too short is better than too long. Realize that it will take quite a few miles to adapt to the shorter crank before it feels natural. Your RPMs will have to increase in order to maintain the same foot speed.

4) Get narrower bars. If you are riding in a pack or racing, this is a nice little benefit. You’ll reduce the amount of space you need in a pack, but also be marginally faster. Just remember that narrower or wider bars than “shoulder width” will make it harder to reach the bars because of how triangles work. So you may need a shorter stem - this will make it slightly harder to handle the bike, but it shouldn’t be an issue.

5) get taller eye protection. Your head accounts for a massive amount of drag. Craning your neck also hurts and reduces the sustainability of the aero position. Find glasses that fit close to your eyes and allow you to duck your head down all the way and look through your eyebrows without getting wind in your eyes. In combination with an aggressive position, this will make a noticeable difference.

6) work on your upper body/core strength. Having a perfect position is less useful if you can’t sustain it when fatigued or when putting down small amounts of power, like when in a pack.

I’m not an expert on aerodynamics, and I cannot say exactly how much this will save you, but I can guarantee you that it will save you more than the difference between a lightweight bike frame and the most aero bike frame.